It is known that an image forming apparatus forms marks on a moving transfer belt with using toner and the marks are detected to detect a deviation in relative positions of the transfer belt and a photosensitive drum. The marks are formed on the transfer belt by the photosensitive drum. Marks are repeatedly formed on the transfer belt along the moving direction of the transfer belt. Accordingly, a mark group extending in the moving direction of the transfer belt is formed. A plurality of mark groups are provided to overlap with each other in a width direction that is perpendicular to the moving direction. The mark groups are detected to detect the deviation in printing positions.
According to the technology, relative deviation in positions of the transfer belt and the photosensitive drum in the moving direction is detected by using the mark groups formed along the moving direction of the transfer belt. Relative deviation in positions of the transfer belt and the photosensitive drum in the width direction is detected by using the mark groups formed to overlap with each other in the width direction of the transfer belt.